In response to, among other things, market conditions and popularity amongst cost-conscious patients, out-of-hospital procedures continue to experience rapid growth. For various reasons, clinicians such as, for example, in office, ambulatory center, dental, non-hospital and hospital settings sometimes administer or supervise the delivery of sedation and analgesia without the services of trained anesthesia providers. This development has led the American Society of Anesthesiologists to issue guidelines for the delivery of sedation and analgesia by non-anesthesiologists. Because the non-hospital setting is in general not as well equipped and staffed as hospitals, malfunctions and complications (such as unintended over-medication leading to loss of consciousness and airway reflexes) may lead to severe outcomes.
A sedation and analgesia system is described in commonly assigned and U.S. patent application Ser. No. 09/324,759, filed Jun. 3, 1999, now U.S. Pat. No. 6,807,965. This system safely provides patients undergoing painful, uncomfortable or otherwise frightening (anxiety inspiring) medical or surgical procedures with sedative, analgesic, and/or amnestic drugs in a way that reduces the risk of overmedication, in both non-hospital and hospital settings. As this system may be used in settings where users may not be trained anesthesia providers skilled in resuscitation and airway management and where complications or malfunctions may have more severe repercussions, the number of potential failure modes was systematically reduced by elimination and/or mitigation. Mitigation was partly accomplished by careful design of the fail safe module for the sedation and analgesia system. Thus, the sedation and analgesia system may be safer than anesthesia machines for use in both non-hospital and hospital environments and may be safely operated by individuals other than trained anesthesia providers such as, for example, trained physicians, or other licensed clinicians and operators.
Anesthesia machines are mainly designed for inhalational anesthesia. In general, as a legacy from earlier anesthesia machine designs that were entirely pneumatic and did not require electrical power to operate. loss of electrical power in current anesthesia machines will not interrupt delivery of anesthetic gases and vapors. In contrast, one embodiment of the sedation and analgesia system described in the '759 application, now U.S. Pat. No. 6,807,965, uses only intravenous anesthetics and no inhalational anesthetics and requires electrical power to operate. During sedation and or analgesia, continued safety in the absence of an anesthesia provider is paramount. These safety systems often employ a set of complicated features to prevent anesthesia machines from being switched off during an anesthetic.
Existing fail-safe systems used on anesthesia machines have the ability to fall back on an all-pneumatic operation mode of operation and may not be applicable to the needs of a sedation and analgesia or total intravenous anesthesia system requiring electrical power to operate. Furthermore, because the sedation and analgesia system is also designed for use by non-anesthesia providers, the consequences of equipment failure may be more severe and thus fail safe systems with a higher reliability that those used on anesthesia machines designed for use by anesthesia providers are required.
Due to the importance of patient safety, test modes for drug delivery devices have long been accepted as an important feature. However, existing fail-safe systems may not take into account the specific requirements that the fail-safe system itself may need to be tested to attain a high-reliability sedation and analgesia system. Simulating a failure to test the fail-safe system for a sedation and analgesia system may be disruptive and cause the system to power down upon detection of the simulated failure. Upon termination of the simulated failure, if the system was powered down, the system will power up and cause further disruption, especially if the power-up, including power-up on self test (POST) routines, takes a long time to complete. Therefore, a need has arisen for a fail-safe module that may be tested without untoward system disruption, in order to confirm proper function of the fail-safe system in a high-reliability sedation and analgesia system.
Further fail-safe systems implement methods of incorporating redundant constituent elements (modules) into the systems. A further need has arisen for a watchdog system integral with a sedation and analgesia system that powers down the sedation and analgesia system in the event of a detected malfunction.